| Reinforced concrete structures in the marine environment are highly susceptible to corrosion of reinforcement due to chloride salt erosion,resulting in reduced durability of the structure and seriously endangering the safety of the structure.Fiber-Reinforced Polymer(FRP)has many advantages such as light weight and high strength,convenient construction,good fatigue performance,and excellent corrosion resistance.The use of FRP reinforcement instead of steel to form FRP reinforced concrete structures holds the promise of fundamentally solving the problem of structural corrosion while reducing the total life cycle cost of the structure.However,the conventional pultruded FRP stirrups have shortcomings such as low strength at the bent portion and relying on the overlapping of the stirrups to transfer force,and thus leading to bonding and anchorage failure,which prevent the high strength of FRP material from being fully utilized and hinder the promotion and application of FRP reinforced concrete structures.In order to solve the problems of conventional pultruded stirrups,this research group proposed continuous fiber GFRP(Glass Fiber-Reinforced Polymer)stirrups.The continuous fiber GFRP stirrups is produced by the fiber winding process,featuring high strength at bent portion and continuous tensile fiber.The new type stirrups do not rely on the overlapping of stirrups legs to transform tensile force,and the the application of this new type of stirrups in concrete beams can improve the shear behavior of FRP reinforced concrete beams by improving the strength of the stirrups while avoiding bond slip and better utilizing the high strength characteristics of FRP materials.In this paper,continuous fiber GFRP stirrups are taken as the object of study,the basic mechanical properties of stirrups are investigated and the corresponding strength calculation methods are proposed,based on the stress state of stirrups in concrete beams.And then,shear performance tests were carried out on concrete simply supported beams with continuous fiber GFRP stirrups,and the effects of various parameters on the shear behavior of the beams were discussed through careful observation of the test phenomena and in-depth analysis of the test results.Then,the finite element simulation of the shear behavior of the beam was further carried out,and the shear capacity calculation model of the continuous fiber GFRP stirrups reinforced beams was proposed on the basis of the test and finite element simulation.The main research contents and conclusions of this paper are as follows:(1)For the possible fracture portions of FRP stirrups,tensile tests on the tensile properties at the bent portion and the shear-tension properties of the straight portion of continuous fiber GFRP stirrups bars were carried out to investigate the influence of the cross-section dimensions of the stirrups and the inclination angle of the diagonal critical cracks in concrete beams on their mechanical properties,the test results indicated that the tensile strength at bent portion was significantly improved compared with pultruded stirrups,the ratio of bent portion strength over tensile strength at the straight portion was approximately 0.6～0.85,the shear-tensile strength at the straight portion over the tensile strength was approximately 0.52～0.71,and based on the tests,a model for the calculation of the tensile strength at the bent portion and the shear-tension strength at the straight portion of the stirrups was proposed.(2)Experimental test on the shear behavior of concrete beams reinforced with continuous fiber GFRP stirrups was carried out,and the shear performance test of concrete beams with continuous fiber GFRP stirrups was carried out to compare the shear behavior of continuous fiber GFRP stirrups reinforced beams with that of beams with pultruded stirrups.The results show that the continuous fiber GFRP stirrups can better control the development of diagonal cracks and effectively improve the shear capacity of beams,and the feasibility and effectiveness of continuous fiber GFRP stirrups applied to concrete beams have been verified.On this basis,the effect of shear-to-span ratio,stirrup spacing,and longitudinal reinforcement ratio on the shear behavior of the beams was further investigated through the shear test of beams.(3)In order to investigate the shear size effect of concrete beams reinforced with continuous fiber GFRP stirrups and FRP rebars,shear tests were carried out on three types of beams with different cross-sectional heights.The effect of crack development on the strain distribution of the stirrups was analyzed by arranging multiple strain gauges on the shear reinforcement,the shear load carried by the beam is further decomposed into the shear carried by the concrete and by the stirrups,and the effect of shear reinforcement on the shear carried by the concrete was revealed.The results showed that for beams with pultruded stirrups the nominal shear stress decreased as as the depth of beam increased,while the nominal shear stress of beams with continuous fiber stirrups increased,the shear size effect did not exhibited within a certain depth range.(4)Based on DIANA software,a finite element model of the concrete beam reinforced with continuous fiber GFRP stirrups was developed and the parametric analysis was carried out;By simplifying and analyzing the failure mechanism obtained from the shear test and combining the finite element analysis results,a shear capacity prediction model for the concrete beams reinforced with continuous fiber GFRP stirrups was proposed,comparison of the predicted results with experimental results and finite element simulations shows that the model has better accuracy than the existing model for FRP reinforced concrete beams... |
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